The Regimental March Past was the title song from the movie The Longest Day,
written by Paul Anka.

The Longest Day

Many men came here as soldiers
Many men will pass this way
Many mean will count the hours

As they live the longest day

Many men are tired & weary
Many men are here to stay
Many men won’t see the sunset
When it ends the longest day

(x2):
The longest day, the longest day

This will be the longest day
Filled with hopes & filled with fears
Filled with blood & sweat & tears
Many men, the mighty thousands
Many men to victory
Marching on, right into battle

In the longest day in history